support tokio's tracing feature

[Alex Chi Z.]

error: failed to select a version for `madsim-tokio`.
    ... required by package `risingwave_ctl v0.1.9 (/Users/skyzh/Work/risingwave/src/ctl)`
    ... which satisfies path dependency `risingwave_ctl` (locked to 0.1.9) of package `risingwave_cmd v0.1.9 (/Users/skyzh/Work/risingwave/src/cmd)`
versions that meet the requirements `=0.2.0-alpha.3` (locked to 0.2.0-alpha.3) are: 0.2.0-alpha.3

the package `risingwave_ctl` depends on `madsim-tokio`, with features: `tracing` but `madsim-tokio` does not have these features.

we may see if we can pass this feature flag to tokio.

[Runji Wang]

Oops, I'll add this feature soon. As a workaround, you can add tokio = { version = "1", features = ["tracing"] } to Cargo.toml to enable this feature. 😅